1. Field of the Invention
This invention relates to integrated circuit (IC) interconnections. More particularly, it relates to IC interconnections utilizing high frequency ultrasonic energy.
2. Description of the Prior Art
The standard technique for making circuit interconnections for plastic encapsulated semiconductor devices utilizes the bonding of metals, for example, gold wire to aluminum or aluminum alloy surfaces (e.g. bond pads). The bond or weld formed eventually results in an intermetallic structure of several possible phases, depending on time and temperature and dictated by diffusion behavior. The highest bond strength will be obtained by initiating the maximum intermetallic coverage.
Contaminated surfaces, unfeasibly low temperatures and nonoptimum bonding parameters all contribute to less than adequate reaction of the gold and aluminum surfaces. The maximum bond strength and highest quality bond is obtained through optimum phase growth. Hence, a bonding process is needed to optimize the reactivity of the bonding materials, e.g. gold and aluminum. Additionally, it would be advantageous to achieve a process wherein lower temperatures and shorter bonding times could be achieved for greater processing flexibility. A process allowing ambient temperature would be extremely desirable.
In addition, a particular problem exists with aluminum alloys (e.g. Al, 2% Cu; or Al, 1% Si, 0.5% Cu). With aluminum alloys even greater reactivity retardation is experienced, thus ultimately damaging the bond strengths involving aluminum alloys.
What is needed is a process which facilitates optimum reactivity of metals such as gold and aluminum in the bonding process for greater (perhaps even 100%) coverage of the cross-sectional area of the bond. Also needed is a process which allows for greater parameter flexibility, such as lower (even ambient) temperatures and/or shorter bonding times and/or lower pressures.